This invention relates to novel monohydroxylated diene polymers which are suitable for use in a variety of applications including adhesives, sealants, coatings, modification of other polymers or asphalt, etc., as well as to be further functionalized to produce useful polymers. More specifically, the invention relates to particular epoxidized monohydroxylated polydiene polymers and their epoxidized derivatives.
Monohydroxylated polydienes are known. Most of these polymers are homopolymers of one diene or another. For example, monohydroxlated polybutadienes are known in the art for use in adhesive formulations. U.S. Pat. No. 4,242,468 describes solventless polyurethane coatings having improved flexibility resulting from incorporation of monohydroxylated polybutadienes. Epoxidized versions of hydroxylated polybutadienes are known as well. Low viscosity epoxidized polydiene polymers are also known, especially for use in adhesives. Such polymers are described in commonly assigned U.S. Pat. Nos. 5,229,464 and 5,247,026.
While the low viscosity polymers of the prior art are useful in applications where aliphatic epoxies are generally employed., they suffer the disadvantage of not being reactive via a broader class of chemistry. Further, epoxidation is costly and many examples of the prior art required high levels of epoxy functionality to be of utility. Incorporation of a more economical moiety which would provide the same or broader chemical utility is highly desirable. The present invention provides polymers which overcome the disadvantages of the aforementioned limited chemical reactivity. Further, in applications requiring epoxy functionality for chemical compatibility these polymers reduce the necessary epoxy levels.
This invention is a monohydroxylated polydiene polymer which is comprised of at least two polymerizable ethenically unsaturated hydrocarbon monomers wherein at least one is a diene monomer which yields unsaturation suitable for epoxidation. The invention also contemplates partially unsaturated and/or epoxidized derivatives of these novel monohydroxylated polydiene polymers. The hydroxylated polymers are preferably block copolymers of at least two diene monomers, preferably isoprene and butadiene, and, optionally, a vinyl aromatic hydrocarbon wherein a hydroxyl group is attached at one end of the polymer molecule. These polymers may be hydrogenated or unhydrogenated but they are preferably epoxidized.
The preferred monohydroxylated polydiene polymer of the present invention has the structural formula
(HO)xxe2x80x94Axe2x80x94Szxe2x80x94Bxe2x80x94(OH)yxe2x80x83xe2x80x83(I)
wherein A and B are polymer blocks which may be homopolymer blocks of conjugated diolefin monomers, copolymer blocks of conjugated diolefin monomers, or copolymer blocks of diolefin monomers and monoalkenyl aromatic hydrocarbon monomers. These polymers may contain up to 60% by weight of at least one vinyl aromatic hydrocarbon, preferably styrene. Generally, it is preferred that the A blocks should have a greater concentration of more highly substituted aliphatic double bonds than the B blocks have. Thus, the A blocks have a greater concentration of di-, tri-, or tetra-substituted unsaturation sites (aliphatic double bonds) per unit of block mass than do the B blocks. This produces a polymer wherein the most facile epoxidation occurs in the A blocks. The A blocks have a molecular weight of from 100 to 6000, preferably 500 to 4,000, and most preferably 1000 to 3000, and the B blocks have a molecular weight of from 1000 to 15,000, preferably 2000 to 10,000, and most preferably 3000 to 6000, S is a vinyl aromatic hydrocarbon block which may have a molecular weight of from 100 to 10,000, x and y are 0 or 1. Either x or y must be 1, but only one at a time can be 1, z is 0 or 1. Either the, A or the B block may be capped with a miniblock of polymer, 50 to 1000 molecular weight, of a different composition, to compensate for any initiation, tapering due to unfavorable copolymerization rates, or capping difficulties. These polymers may be epoxidized such that they contain from 0.1 to 7.0 milliequivalents (meq) of epoxy per gram of polymer.
Polymers containing ethylenic unsaturation can be prepared by anionically copolymerizing one or more olefins, particularly diolefins, by themselves or with one or more alkenyl aromatic hydrocarbon monomers. The copolymers may, of course, be random, tapered, block or a combination of these.
Diene containing polymers, having residual unsaturation suitable for epoxidation, may also be obtained by other means of polymerization, such as by cationic polymerization or free radical polymerization. Using cationic polymerization, monomers such as substituted 1-butenes, 1-pentenes and dienes such as isoprene and butadiene can be copolymerized. Like anionic polymerization, living cationic polymerization allows the copolymers to be block copolymers such that the residual diene double bond can be localized within the polymer. Dienes may be polymerized together with acrylic monomers by initiation with a free radical initiator, such a peroxide or AIBN. For pressure sensitive adhesive applications, monomers such as n-butyl acrylate, 2-ethyl-hexyl acrylate and isoprene may be used, and other modifying monomers, such as acrylic acid or 2-hydroxy-ethyl acrylate may also be used. Other polymerization methods including coordination/insertion mechanisms such as Ziegler-Natta polymerizations, metallocene polymerizations, and metathesis polymerizations can also be used to make polymers such as these.
The polymers containing ethylenic unsaturation or both aromatic and ethylenic unsaturation may be prepared using anionic initiators or polymerization catalysts. Such polymers may be prepared using bulk, solution or emulsion techniques. When polymerized to high molecular weight, the polymer containing at least ethylenic unsaturation will, generally, be recovered as a solid such as a crumb, a powder, a pellet or the like. When polymerized to low molecular weight, it may be recovered as a liquid.
In general, when solution anionic techniques are used, copolymers of conjugated diolefins, optionally with vinyl aromatic hydrocarbons, are prepared by contacting the monomer or monomers to be polymeized simultaneously or sequentially with an anionic polymerization initiator such as group IA metals, their alkyls, amides, silanolates, napthalides, biphenyls or anthacenyl derivatives. It is preferred to use an organo alkali metal (such as sodium or potassium) compound in a suitable solvent at a temperature within the range from about xe2x88x92150xc2x0 C. to about 300xc2x0 C., preferably at a temperature within the range from about 0xc2x0 C. to about 100xc2x0 C. Particularly effective anionic polymerization initiators are organo lithium compounds having the general formula:
RLin
wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbon radical having from 1 to about 20 carbon atoms and n is an integer of 1 to 4.
Conjugated diolefins which may be polymerized anionically include those conjugated diolefins containing from about 4 to about 24 carbon atoms such as 1,3-butadiene, isoprene, piperylene, methylpentadiene, phenyl-butadiene, 3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadiene and the like. Isoprene and butadiene are the preferred conjugated diene monomers for use in the present invention because of their low cost and ready availability. Alkenyl (vinyl) aromatic hydrocarbons which may be copolymerized include vinyl aryl compounds such as styrene, various alkyl-substituted styrenes, alkoxy-substituted styrenes, vinyl napthalene, alkyl-substituted vinyl napthalenes and the like.
The monohydroxylated polydienes are synthesized by anionic polymerization of conjugated diene hydrocarbons with lithium initiators. This process is well known as described in. U.S. Pat. No. 4,039,593 and Re. No. 27,145 which descriptions are incorporated herein by reference. Polymerization commences with a monolithium initiator which builds a living polymer backbone at each lithium site. Typical monolithium living polymer structures containing conjugated diene hydrocarbons are:
Xxe2x80x94Axe2x80x94Bxe2x80x94Li
Xxe2x80x94Axe2x80x94Bxe2x80x94Axe2x80x94Li
wherein B represents polymerized units of one conjugated diene hydrocarbon such as butadiene, A represents polymerized units of another conjugated diene such as isoprene, and either A or B may contain one or more vmyl aromatic compounds such as styrene, and X is the residue of a monolithium initiator such as sec-butylithium. The hydroxyl groups are added by terminal capping the polymerization with oxiranes such as ethylene oxide followed by termination with methanol.
Monohydroxy diene polymers can also be made using a mono-lithium initiator which contains a hydroxyl group which has been blocked as the silyl ether. Details of the polymerization procedure can be found in U.S. Pat. No. 5,396,745, which is herein incorporated by reference. A suitable initiator is hydroxyporoyllithium in which the hydroxyl group is blocked as the tert-butyl-dimethylsilyl ether. This mono-lithium initiator can be used to polymerize isoprene or butadiene in hydrocarbon or polar solvent. The living polymer is then terminated with methanol. The silyl ether is then removed by acid catalyzed cleavage in the presence of water yielding the desired monohydroxy polydiene polymer.
When one of the conjugated dienes is 1,3-butadiene and it will be hydrogenated, the anionic polymerization of the conjugated diene hydrocarbons is typically controlled with structure modifiers such as diethylether or glyme (1,2-diethoxyethane) to obtain the desired amount of 1,4-addition. As described in U.S. Pat. No. Re 27,145 which is incorporated by reference herein, the level of 1,2-addition of a butadiene polymer or copolymer can greatly affect elastomeric properties after hydrogenation. The hydrogenated polymers exhibit improved heat stability and weatherability in the final adhesive, sealant or coating.
The most highly preferred polymers for use herein are diblock polymers which fall within the scope of formula (I) above. The overall molecular weight of such diblocks may range from 1500 to 20000, preferably 3000 to 7000. Either of the blocks in the diblock may contain some randomly polymerieed vinyl aromatic hydrocarbon as described above. For example, where I represents isoprene, B represents butadiene, S represents styrene, and a slash (/) represents a random copolymer block, the diblocks may have the following structures:
I-B-OH I-B/S-OH I/S-B-OH I-I/B-OH or
B/I-B/S-OH B-B/S-OH I-EB-OH I-EB/S-OH or
I-S/EB-OH I/S-EB-OH HO-I-S/B HO-I-S/EB
where EB is hydrogenated butadiene, -EB/S-OH means that the hydroxyl source is attached to a styrene mer, and -S/EB-OH signifies that the hydroxyl source is attached to a hydrogenated butadiene mer. This latter case, -S/EB-OH, requires capping of the S/EB xe2x80x9crandom copolymerxe2x80x9d block with a mini EB block to compensate for the tapering tendency of the styrene prior to capping with ethylene oxide. These diblocks are advantageous in that they exhibit lower viscosity and are easier to manufacture than the correponding triblock polymers. It is preferred that the hydroxyl be attached to the butadiene block because the epoxidation proceeds more favorably with isoprene and there will be a separation between the functionalities on the polymer. However, the hydroxyl may also be attached to the isoprene block if desired. This produces a more surfactant-like molecule with less load bearing capacity. The isoprene blocks may also be hydrogenated.
Certain triblock copolymers are also preferred for use herein. Such triblocks usually include a styrene block or randomly copolymerized styrene to increase the polymers glass transition temperature, compatibility with polar materials, strength, and room temperature viscosity. These triblocks include the following specific structures:
I-EB/S-EB-OH I-B/S-B-OH I-S-EB-OH I-S-B-OH or
I-I/S-I-OH I-S-I-OH B-S-B-OH B-B/S-B-OH or
I-B/S-I-OH I-EB/S-I-OH or
I-B-S-OH I-EB-S-OH HO-I-EB-S
The latter group of polymers specified in the last line above wherein the styrene block is external are represented by the formula
(HO)xxe2x80x94Axe2x80x94Bxe2x80x94Sxe2x80x94(OH)yxe2x80x83xe2x80x83(II)
where A, B, S, x, and y are as described above.
Epoxidation of the base polymer can be effected by reaction with organic peracids which can be preformed or formed in situ. Suitable preformed peracids include peracetic and perbenzoic acids. In situ formation may be accomplished by using hydrogen peroxide and a low molecular weight fatty acid such as formic acid. Alternatively, hydrogen peroxide in the presence of acetic acid or acetic anhydride and a cationic exchange resin will form a peracid. The cationic exchange resin can optionally be replaced by a strong acid such as sulfuric acid or p-toluenesulfonic acid. The epoxidation reaction can be conducted directly in the polymerization cement (polymer solution in which the polymer was polymerizedy or, alternatively, the polymer can be redissolved in an inert solvent. These methods are described in more detail in U. S. Pat. Nos. 5,229,464 and 5,247,026 which are herein incorporated by reference. In particular, we have found that when using peracetic acid for the epoxidation, the rate of epoxidation of residual aliphatic double bonds in polyisoprene and polybutadiene is the following, 1,4-polyisoprene mers (tri-substituted aliphatic double bonds) greater than 1,4-polybutadiene mers (1,2di-substituted aliphatic double bonds) greater than 3,4-polyisoprene mers (1,1-di-substituted aliphatic double bonds) greater than 1,2-polybutadiene mers (mono-substituted aliphatic double bonds). Neither 1,2-polybutadiene mers nor polystyrene mers have been observed to epoxidize.
The molecular weights of linear polymers or unassembled linear segments of polymers such as mono-, di-, triblock, etc., arms of star polymers before coupling are conveniently measured by Gel Permeation Chromatography (GPC), where the GPC system has been appropriately calibrated. For anionically polymerized linear polymers, the polymer is essentially monodisperse (weight average molecular weight/number average molecular weight ratio approaches unity), and it is both convenient and adequately descriptive to report the xe2x80x9cpeakxe2x80x9d molecular weight of the narrow molecular weight distribution observed. Usually, the peak value is between the number and the weight average. The peak molecular weight is the molecular weight of the main species shown on the chromatograph. For polydisperse polymers the weight average molecular weight should be calculated from the chromatograph and used. For materials to be used in the columns of the GPC, styrene-divinyl benzene gels or silica gels are commonly used and are excellent materials. Tetrahydrofuran is an excellent solvent for polymers of the type described herein. A refractive index detector may be used.
If desired, these block copolymers can be partially hydrogenated. Hydrogenation may be effected selectively as disclosed in U.S. Pat. No. Reissue 27,145 which is herein incorporated by reference. The hydrogenation of these polymers and copolymers may be carried out by a variety of well established processes including hydrogenation in the presence of such catalysts. as Raney Nickel, nobel metals such as platinum and the like, soluble transition metal catalysts and titanium catalysts as in U.S. Pat. No. 5,039,755 which is also incorporated by reference. The polymers may have different diene blocks and these diene blocks may be selectively hydrogenated as described in U.S. Pat. No. 5,229,464 which is also herein incorporated by reference. Partially unsaturated hydroxylated polymers are preferred for further functionalization such as to make the epoxidized polymers of this. invention. They can also be chlorinated, brominated, or reacted with maleic anhydride, or used directly for vulcanization or reaction with amino resins. The partial unsaturation preferably is such that 0.1 to 7 meq/g of aliphatic double bonds remain for subsequent epoxidation.
The epoxidized derivatives of these polymers may be used in pressure sensitive adhesives, films, sealants, coatings, structural adhesives, laminating adhesives, pressure sensitive structural adhesives, printing plates, and in the modification of other polymers and/or asphalt (i.e., blends with other polymers andor asphalt for the purpose of altering the properties of those materials). The unepoxidized polymers may be used in applications for which other monohydroxlated polymers have been commonly used, including as part of a binder system for adhesives. However, their primary utility is to be functionalized, such as by epoxidation, to form useful functionalized derivatives.